Ribonucleic acid interference (RNAi) is one of the most exciting discoveries in biology in modern times and represents a revolution in the analysis of gene function. At present, genome-wide RNAi screens are becoming an increasingly important part in the process of target discovery. However, there is a lack of apparatuses and methods for the efficient tranfection of biologically relevant cell types at a sufficient throughput. For example, lipid-based methods can deliver in terms of throughput, but are unable to efficiently transfect most biologically relevant cell types. Methods based on conventional electroporation can transfect a wide range of primary and hard-to-transfect cell types, but are unable to do so at a price, efficiency and throughput required.
Electroporation is an increase the in the electrical conductivity and permeability of the cell membrane caused by an externally applied electrical field. In molecular biology, electroporation is used to introduce substances into a cell. For example, a nucleic acid can be introduced into a cell to change the cell's function. Electroporation is generally useful for introducing nucleic acids or other chemical or physical entities into tissue culture cells, including mammalian cells as well as to targeted organs in the living body. Electroporation applications include tumor treatment, gene therapy, cell-based therapy, and drug discovery.
In traditional electroporation techniques, electroporators create an electric current and pass it through a cell solution in a cuvette containing e.g. two metal electrodes on its sides. The cell suspension contained in the cuvette is mixed with a plasmid to be introduced into the cells. The cuvette is inserted into an electroporator, which applies a voltage (for example, 240 volts) to the electrodes and creates an electric field in the cell solution allowing the plasmid to enter the cell. After the cell solution is electroporated, the cells have to be handled carefully until they have had a chance to divide producing new cells that contain reproduced plasmids.
In many current electroporation practices, cells are detached from the cell culture vessel, placed in suspension, and transferred to cuvettes for electroporation as described above. This process is labor intensive and limits throughput and effectiveness. In addition, the electroporation step itself may cause significant stress to the cells and in combination with elaborate handling of cells such as scraping, digestion, transfer, pipetting and the like. As a result, high rates of cell morbidity and mortality are often observed.